Research on heat storage differences between the upper body and
lower body for paraplegic athletes is sparse. However, a few studies
have reported heat storage when evaluating the effectiveness of various
cooling interventions. Webborn et al. (1) examined the effects of two
cooling strategies (pre-cooling and cooling during exercise) on
thermoregulatory responses of tetraplegic athletes. The authors, using a
repeated measures design, examined two strategies during 28 minutes of
intermittent arm crank exercise. The authors reported no difference (p =
0.39) in heat storage between a control trial (3.62 [+ or -] 0.4 J x
[g.sup.-1]) and either intervention during pre-cooling (4.17 [+ or -]
0.4 J x [g.sup.-1]) and cooling during exercise (3.15 [+ or -] 0.35 J x
[g.sup.-1]).

Price and Campbell (2) examined upper- v. lower-body skin
temperature in paraplegic athletes. Results from arm ergometry exercise
indicated that paraplegic athletes (v. able-bodied athletes), showed
lower skin temperatures for the lower body after 90 minutes of work at
80% of peak heart rate (HR) in room temperature . However, upper-body
skin temperature was also lower for the paraplegic group v. the
able-bodied group. The authors speculated that this could be due to
atrophied musculature and/or an atrophied vascular system below the
level of lesion. (2) Unfortunately no information was provided on rectal
or oesophageal temperatures (two accepted measures of core body
temperature), so heat storage cannot be calculated for the upper-body
and lower-body regions. Furthermore, no effort was made to match groups
for fitness.

In general, paraplegics seem to adequately regulate body core
temperature at rest; however, they show a greater increase in core
temperature when compared with able-bodied (AB) subjects during exercise
and/or working conditions work. (3) Furthermore, it has been
demonstrated that individuals with a T6 (thoracic) lesion and below are
subjected to smaller increases in core temperature than those
individuals with a lesion above T6. These individuals, in turn,
demonstrate smaller increases than those with tetraplegia (cervical
lesions). (4) Individuals with a spinal cord injury at or above T6 are
prone to episodes of autonomic hyperreflexia when exposed to
incompensable stimuli. These responses have been well documented by
Jacobs and Nash, (5) who further suggest that a common stimulus amongst
others is a sudden rise in core temperature.

There seems to be a lack of knowledge regarding heat storage
differences between upper-body ([HS.sub.upper]) and lower-body
([HS.sub.lower]) regions over the period of an exercise bout,
particularly in spinal cord injured athletes (SCI) athletes.
Understanding the heat storage of SCI athletes will illuminate both the
thermal physiology as well as the circulatory function of this group.
Furthermore, enhancing the knowledge of thermal physiology within this
cohort could aid in the development of more effective cooling
interventions. For example, the lower skin temperatures in SCI
participants reported by Price et al. (6) may reflect a higher core
temperature and reduced cutaneous vasodilatation, suggesting less
effectiveness of skin cooling. A reduction in skin cooling has recently
been noted by Pritchett et al., (7) where the authors highlighted a
decrease in sweat response among participants with SCI, which led to a
decreased ability to thermoregulate. This study therefore proposes to
describe the heat storage dynamics over the course of a ~35-minute
graded exercise bout under simulated gymnasium playing conditions
(20[degrees]C [+ or -] 1[degrees]C; 45-65 [+ or -] 0.1% relative
humidity) in both SCI and AB participants.

Method

Participants

Fifteen volunteers gave their informed consent to participate in
this investigation, which had received approval by the University of
Alabama Institutional Review Committee. The group was comprised of 7
paraplegic athletes (SCI) and 8 AB upper-body trained athletes (see
Table I).

AB athletes were wheelchair basketball team members absent of SCI
(N = 4), and the remainder (N = 4) were from the university swimming
team.

Based on an alpha level of 0.05 an effect size of 1.0, a SD of 0.5
J x [g.sup.-1] for heat storage, and a power of 0.80, an a priori power
analysis indicated 7 subjects would be needed. (8)

Exercise tests

Participants visited the laboratory on two separate occasions. On
the first occasion, volunteers performed an incremental arm-crank
exercise (ACE) test to determine V[O.sub.2] peak with gas exchange
indices collected using a Vacumed Vista mini cpx metabolic measurement
system (Vacumed, Vista, CA). This involved two 5-minute submaximal
exercise stages of arm-crank exercise (30 W and 50 W) separated by 1
minute of passive recovery. (9) Once the two submaximal ACE stages and a
rest stage had been completed, volunteers exercised to volitional
exhaustion at a ramp rate of 20 W every 2 minutes from an initial level
of 110 W. All tests were conducted on a cycle ergometer (Monark 850E,
Varberg, Sweden) adapted for upper-body exercise. Participants were
instructed to maintain at least 50 rev. [min.sup.-1] throughout the
test. For the second laboratory visit the exercise test consisted of
multiple stages, beginning at a workload of 35 W. Resistance of each
stage was held constant for 7 minutes. At the end of each stage,
participants had a 1-minute passive recovery. The workload of each stage
increased by 35 W, until such time that heat production exceeded heat
dissipation as evidenced by a sudden increase in the time-slope of the
[T.sub.es]. The increase in [T.sub.es] was identified as critical when
it was greater than 0.2[degrees][C.sup.-1] per minute. (10) Temperature
measures were conducted during the second laboratory visit only.

Temperature measures

On arrival at the laboratory for the incremental test,
thermocouples (Physitemp Instruments INC., Clifton, NJ, USA) were
positioned for measurement of rectal ([T.sub.rec]) and oesophageal
temperatures ([T.sub.es]). The oesophageal thermocouple was inserted
with the following procedure. The inside of the nose of the subject was
swabbed with a mild anaesthetic jelly (7.5% Benzocaine), and a light
covering of jelly was also placed on the distal end of the thermistor. A
single spray of a topical anaesthetic (Cetacaine, 14% Benzocaine,
Cetylite Ind., Pennsauken, NJ USA) was sprayed on the back of the
throat. After 2 minutes, the volunteers advanced the oesophageal probe
through the nose and to the pharynx. At this point the probe was
withdrawn slightly, and the volunteer was then requested to drink water
through a right-angle straw and at the same time the probe was advanced
into the oesophagus to a length of one-fourth of the volunteer's
supine height and then taped to the nose and across the shoulder. (11) A
flexible rectal thermocouple ([T.sub.rec]) probe was self-inserted ~8 cm
beyond the anal sphincter. The rectal probe was securely taped, and the
thermocouple wire was passed over the back of the wheelchair to minimise
interference with arm cranking.

Skin temperature ([T.sub.sk]) was continuously monitored from
thermocouples placed at the following sites: forehead, forearm, upper
arm, back, chest, thigh and calf. Thermocouples were attached to the
skin using adhesive tape, cut around the head of the thermocouple, which
held thermocouples in place without adding insulation.

Heat storage was calculated from the formula by Havenith et al.
(12) Heat storage for the upper-body region was calculated using
[DELTA][T.sub.es] and [DELTA][T.sub.sk] by tabulating the weighted mean
skin temperature between forearm (20%), back (40%) and chest (40%).
Lower-body heat storage was calculated using [DELTA][T.sub.rec] and
[DELTA][T.sub.sk], which was calculated using the mean skin temperature
(thigh 70% and calf 30%) from the formula of Ramanathan. (13) Heat
storage for each region was calculated where:

Heat storage for the upper body ([HS.sub.upper]) and heat storage
for the lower body ([HS.sub.lower]) were compared using paired t-tests.
Level of significance was set at alpha [less than or equal to] 0.05. A
one-way analysis of variance was used to compare the difference between
SCI athletes and matched AB athletes. Furthermore, to allow for a
depletion of subjects due to differentiated termination time, a harmonic
mean was calculated and analysis over time using a repeated measures
ANOVA with a Bonferroni post hoc test employed where necessary.

Results

Descriptive statistics (means and standard deviations) for SCI and
AB are presented in Table I. There was no difference in absolute
V[O.sub.2] peak, stature and age. However, body mass was significantly
different between groups (p = 0.03). AB athletes were matched to SCI
athletes based on activity status, V[O.sub.2] peak, with 3 of the 8 AB
being active participants in college wheelchair basketball.
Thermoregulatory responses during exercise for SCI and AB were compared
and presented graphically. There was no significant difference (p =
0.06) in [T.sub.es] between SCI (38.0 [+ or -] 0.2[degrees]C) and AB
(37.6 [+ or -] 0.4[degrees]C) (Fig. 1). However, it was noted that there
was a greater increase in [T.sub.es] for SCI within the last two stages
of the exercise bout. [T.sub.rec] (Fig. 2) for both groups were similar
with no statistical difference between groups (p > 0.05). Figures are
reported with the sample size, as the increasing intensity lead to a
depleted sample size as individual termination points were reached. One
subject (T3 lesion level) completed two stages, and was matched with an
AB subject that completed two stages. Only two subjects could not
complete the final stage (90 W). Data are presented for all stages that
more than 70% of the subjects completed. Analysis of variance indicated
that mean skin temperature for the lower body ([M.sub.sk]) (Fig. 4) for
SCI subjects was significantly higher than for AB throughout the
exercise bout (p = 0.006). However, mean skin temperature for the upper
body (Fig. 3) was significantly different than for the first (30 W)
stage (SCI: 35.2 [+ or -] 0.9C, AB: 33.4 [+ or -] 0.8[degrees]C) and
second stage (50 W) (SCI: 33.4 [+ or -] 0.9[degrees]C, AB: 33.7 [+ or -]
1.0[degrees]C). However, for the last two stages, there were no
significant differences detected between groups. There was no
significant difference observed between upper body and lower body for
heat storage between SCI and AB athletes (p=0.38, Fig. 5). Furthermore,
it is interesting to note that there was a significant difference
observed between [HS.sub.upper] and [HS.sub.lower] body for SCI (0.82 [+
or -] 0.59 J x [g.sup.-1] and 0.47 [+ or -] 0.33 J x [g.sup.-1]) (p =
0.04) and also for AB (0.80 [+ or -] 0.61 J x [g.sup.-1] and 0.27 [+ or
-] 0.22 J x [g.sup.-1]) (p = 0.03). Heat storage for SCI and AB per
stage for both upper and lower body are presented in Figs 6 A and B,
respectively. There was no significant difference for HS between stages
for either group.

[FIGURE 1 OMITTED]

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

Discussion

The current study was undertaken in a common mild environment
(simulation of a typical wheelchair basketball playing environment)
under exercise conditions that were intended to simulate the duration
and intensity of a typical competition half. Our intent was to maintain
high ecological validity throughout the investigation in order to make
the results of this study inferable to an active SCI population
partaking in wheelchair sports. It has been stated that individuals with
SCI have a compromised ability to thermoregulate, which can lead to
magnified risk of thermal injury. (14) The purpose of this paper was to
add to the understanding of the thermophysiology of heat storage in SCI
athletes.

[FIGURE 4 OMITTED]

[FIGURE 5 OMITTED]

All subjects were matched based on fitness. Three AB subjects had
experienced training identical to the SCI group participating on the
same wheelchair basketball team and swimming teams (absolute V[O.sub.2]
peak is presented in Table I). Buresh et al. (15) suggested body mass
and heat storage in AB athletes are significantly correlated. However,
it is difficult to match these two populations (SCI and AB) for body
mass.

As heat storage is a composite of both core temperature and skin
temperature changes, for this study heat storage was compared between
upper and lower body. There were lower heat storage values for the lower
body compared with the upper body for both groups. However, there was no
significant difference between groups. Reduced heat storage for the
lower body might have been due to the lack of muscular contraction in
the lower body. Therefore, there was little metabolic heat production.
[HS.sub.lower] was comprised of [T.sub.rec] and [M.sub.sk] (calf and
thigh). There was no significant difference in the change in [T.sub.rec]
between the SCI and AB groups. This could account for little differences
detected between the two populations. Both groups also demonstrated
little difference for [HS.sub.upper]. Greater HS for the upper body
observed for both groups might have been due to the nature of the
exercise mode. It could also be speculated that due to the SCI athletes
having a greater sweat response above their level of lesion. It has been
demonstrated that at rest SCI athletes have warmer skin temperature,
which enables an earlier onset of sweating, and therefore earlier skin
cooling when compared with AB athletes. (16) This upper-body adaptation
to an impaired thermoregulatory ability might help compensate for the
lower body inability to dissipate stored heat.

[FIGURE 6 OMITTED]

[M.sub.sk] temperature (Fig. 3) for the upper body was higher than
the lower-body skin temperature in SCI. Also, SCI experienced higher
mean skin temperature in both the upper and lower body than did the AB.
This is in accordance with Fitzgerald et al., (17) who noted that
volunteers with SCI who performed prolonged exercise at 24-25[degrees]C
experienced an increase of ~0.7[degrees]C (in core temperature). It was
suggested that the increase in [M.sub.sk] was due to heat being
generated from the working muscles, which was then transferred to the
skin. Heat from the insensate skin would not be able to be dissipated,
thus this would result in an increase in skin temperature.

One of the more extensively compiled research composites is that of
sweat response between AB and SCI individuals and between different
levels of SCI. (3,4,18) A reduction in whole-body sweating leads to
greater increase in core temperature at rest, and a greater drive for
sweating for a given environmental temperature. (19,20) The current
investigation reported slightly elevated [T.sub.es] for SCI athletes
initially (37.1 [+ or -] 0.4[degrees]C) compared with AB (36.9 [+ or -]
0.2[degrees]C). Similar responses were recorded for [T.sub.rec] (SCI =
37.2 [+ or -] 0.5[degrees]C and AB = 37.4 [+ or -] 0.3[degrees]C).
However, it could be noted that the fluctuation in [T.sub.es] and
[T.sub.rec] could quite possibly be due to circadian variation or
day-to-day variations. Trec was late to increase in the SCI athletes,
only showing increase in the last two stages. This could possibly be due
to a lag time experienced in Trec measures, where rectal temperature
measures have been shown to respond more slowly. (11)

Conclusion

In summary, the current study examined the heat storage response
during upper-body high-intensity exercise. Results of this study suggest
SCI and AB athletes were similar with respect to thermoregulation during
arm cranking. SCI athletes tended to store slightly more heat in the
lower body than AB athletes. Both groups also demonstrated little
difference for heat storage in the upper body. Similarly, there was no
significant difference observed for lower-body heat storage values. In a
simulated gymnasium temperature environment it appears the matched
groups demonstrated few meaningful differences in the current paradigm.
Future research should look at more sophisticated observation of heat
transfer like thermography to better understand the dynamics of stored
heat within this population during high-intensity activity.